The development of the new method for manufacturing magnetic cores for electrical machines was necessitated by the need for magnetic core turns having accurate geometrical parameters which would make it possible to meet the efficiency requirements imposed upon magnetic cores of electrical machinery. Another reason for the development of the new method was the desire to automate the magnetic core manufacturing process and use a single piece of equipment for the purpose.
There is known a method for manufacturing coiled magnetic cores (cf. copending U.S. Patent Application Ser. No. 766,918; filed Feb. 9, 1977 having two common inventors with the present application). According to this method, a continuously fed band is coiled edgewise so that a maximum elongation occurs at that edge of the band which forms the external diameter of the coil, whereas there is a uniform decrease in the elongation towards the opposite edge of the band. The coiling of the continuously fed band is done by fluting the band, while maintaining its rectilinear motion. The flutes are then straightened out, whereby the coil is produced.
The method under review is disadvantageous in that the fluting results in an elongation of the band's material; there is a direct relationship between the geometrical parameters of magnetic cores and the relative elongation of the material. The elongation of the fibers of the band's material is at its maximum in the zone of the external diameter of the coil; it must not be in excess of the permissible relative elongation value of the material, otherwise the material will be ruptured in the maximum deformation zones.
The application of the method under review is further limited by the fact that the possibility of such a rupture increases with an increase in the height of the yoke and a decrease in the coil's diameter. This method does not make it possible to manufacture magnetic cores for electrical machinery of all types and sizes.
There is known a device for manufacturing coiled magnetic cores for electrical machines (cf. British Pat. No. 1,114,055). The device comprises a bed whereupon there are mounted a band tensioning means, a straight guide and an arched guide between which there is interposed a shaping member. The bed is provided with a recess receiving a rotary disc carrying uniformly spaced fingers. The device further includes two guide channels one of which is straight and formed by the bed and the straight guide, whereas the second is arched and formed by a portion of the rotary disc and the arched guide. Finally, the device includes a cutter to separate the coil from the rotary disc, and a cam to set the fingers in reciprocating motion.
On the working side of the rotary disc there are recesses shaped as cones or pyramids whose vertices are directed towards the external diameter of the rotary disc. The shaping member is a roll having projections on its outer surface. The projections are spaced uniformly, and their shape corresponds to that of recesses provided in the rotary disc.
When the device is in operation, the projections of the roller are received in the recesses of the rotary disc, and the band is appropriately shaped between them.
The device under review is intended for carrying out a well-known method for manufacturing coiled magnetic cores. According to this method, a flexible band is coiled edgewise by fluting it in the transverse direction without changing the band's thickness. The flutes of the coil thus produced have a maximum perimeter on the side of the internal diameter; the perimeter of the flutes uniformly decreases towards the outer edge. When a magnetic core pack is assembled from such coils, the convex flutes of one turn are received in the concave flutes of the adjacent turn. The presence of the flutes in the finished pack prevents close contact between turns of the magnetic core coil. On straight portions, considerable gaps are produced between the sheets, which cannot be eliminated by pressure molding. Such a loose pack accounts for an unnecessarily great length of the electrical machine, unnecessarily heavy losses of copper, reduced efficiency, and strong magnetic noise.
It is therefor, a principle object of the present invention to improve the quality of coiled magnetic cores and simplify their manufacture.